Stir membrane liquid phase microextraction of tetracyclines using switchable hydrophilicity solvents followed by high-performance liquid chromatography.

A novel approach for stir membrane liquid phase microextraction of tetracyclines from biological fluids was developed. The microextraction procedure assumed in situ formation of microdroplets of a hydrophobic medium-chain fatty acid (extraction solvent) from homogeneous sample solution containing water-soluble medium-chain fatty acid salt by acidification and simultaneous analytes extraction and organic phase separation into pores of stir membrane disk. Obtained large surface area between the extraction solvent and aqueous phase and high porosity of the membrane provided fast extraction and phase separation (extraction time - 5 min) and reducing extraction solvent volume to the order of several µL. The developed approach was applied for the HPLC-UV determination of tetracycline, oxytetracycline and chlortetracycline in biological fluids samples. The calibration graphs were linear over the concentration ranges of 0.1-100 mg L-1 for oxytetracycline, tetracycline and chlortetracycline. Regression coefficients were in the range from 0.994 to 0.998. The LOD values, calculated from the blank tests based on 3σ, were 30 µg L-1 for tetracycline, oxytetracycline and chlortetracycline. The RSD values expressing intra-day and inter-day repeatability were lower than 5% and 8%, respectively.

Homogeneous liquid-liquid microextraction based on primary amine phase separation: A novel approach for sample pretreatment.

A homogeneous liquid-liquid microextraction procedure based on primary amine phase separation was developed as a novel approach for the pretreatment of biological fluids. The procedure assumes primary amine dissolution in the aqueous sample phase, resulting in the creation of a homogeneous sample solution followed by phase separation and analyte extraction in the presence of a polar, water-miscible organic solvent. The phenomenon of primary amine phase separation from homogeneous aqueous solution in the presence of a polar, water-miscible organic solvent was studied in detail and applied for separation and preconcentration in chemical analysis for the first time. The suggested approach was used for the HPLC-UV determination of meropenem as a proof-of-concept analyte in human plasma and serum samples. Under optimal conditions, the detector response of meropenem was linear in the concentration range of 0.1-100.0 mg L-1. The limit of detection was calculated from a blank test based on 3σ, was 0.03 mg L-1.

A rotating cotton-based disk packed with a cation-exchange resin: Separation of ofloxacin from biological fluids followed by chemiluminescence determination.

A novel approach for green and simple solid-phase extraction of ionizable analytes using cation-exchange resin particles packed in a rotating cotton-based disk has been developed and utilized for the chemiluminescence determination of ofloxacin in biological fluids (serum and urine). The use of highly-available cation-exchange resin provided effective separation of analyte from complex sample matrixes and its elution by aqueous electrolyte solution without any organic solvents. Ofloxacin ionization in acidic sample solution allowed to provide effective separation of the analyte for subsequent chemiluminescence detection. The cotton-based disk was characterized by effective wettability. This feature promoted high mass transfer of the analyte to the cation-exchange resin surface at separation step and into elution solution at elution step. The sorption time was decreased to 10 min while the elution time was 5 min. Under the optimal conditions, the detector response for ofloxacin was linear in the concentration range from 9 × 10-8 to 3 × 10-5 mol L-1. The limit of detection, calculated from a blank test based on 3σ, was 3 × 10-8 mol L-1.

An automated salting-out assisted liquid-liquid microextraction approach using 1-octylamine: On-line separation of tetracycline in urine samples followed by HPLC-UV determination.

An automated salting-out assisted liquid-liquid microextraction (SALLME) procedure based on a flow system was developed as new approach for pretreatment of complex sample matrix. In this procedure 1-octylamine was investigated as novel extractant for the SALLME. The procedure involved aspiration of the 1-octylamine and sample solution into a mixing chamber of a flow system followed by their air-bubble mixing resulting to isotropic solution formation. To provide phase separation a salting-out agent solution was added into the mixing chamber. After phase separation, the micellar 1-octylamine phase containing analyte was mixed with methanol and transported to a HPLC-UV system. To demonstrate the efficiency of the suggested approach, the automated procedure was applied for the HPLC-UV determination of tetracycline as a proof-of-concept analyte in human urine samples. Under the optimal conditions, the detector response of the analytes was linear in the concentration ranges of 0.5-20 mg L-1. The limit of detection, calculated from a blank test based on 3σ, was 0.17 mg L-1. The results demonstrate that the developed approach is highly cost-effective, simple and rapid.

An automated magnetic dispersive micro-solid phase extraction in a fluidized reactor for the determination of fluoroquinolones in baby food samples.

An automated magnetic dispersive micro-solid phase extraction procedure in a fluidized reactor was developed for the determination of fluoroquinolone antimicrobial drugs (fleroxacin, norfloxacin and ofloxacin) in meat-based baby food samples. A stepwise injection system was successfully combined with afluidized reactorand applied for the magnetic dispersive micro-solid phase extraction procedure automation. The developed automated procedure involved injection of the sample solution into the fluidized reactor followed by the on-line separation of the analytes from the sample matrix based on fluidized beds strategy using magnetic nanoparticles, elution and determination of the analytes using a high performance liquid chromatography system with fluorescence detection. The floating of the magnetic nanoparticles in a liquid sample phase was accomplished by air-bubbling. In the developed method Zr-Fe-C magnetic nanoparticles were used as an efficient sorbent for the determination of fleroxacin, norfloxacin and ofloxacin. Under the optimal conditions, the calibration graphs were linear over the concentration ranges of 10-1000 µg L-1 for fleroxacin (R2 = 0.996), 5-1000 µg L-1for norfloxacin (R2 = 0.998) and ofloxacin (R2 = 0.998). The limits of detection, calculated from the blank tests based on 3σ, were 3.0 µg L-1forfleroxacin, 1.5 µg L-1for norfloxacin and ofloxacin. The limits of quantification, calculated from the blank tests based on 10σ, were 10 µg L-1 forfleroxacin, 5 µg L-1for norfloxacin and ofloxacin. The method was applied for the determination of fluoroquinolonesin meat-based baby food samples and the results were compared with those obtained by the reference method. The recovery values for all analytes were within of 86-122% range.